Republican lawmakers are raising alarm that Secretary of State John Kerry is putting too much on the table in talks over Iran’s nuclear program — as Tehran reportedly tries to leverage its cooperation in the Islamic State crisis in return for nuclear concessions from the U.S. and its allies, Fox News reports.

The White House denies that any such trade-off is in the works.

“The United States will not be in a position of trading aspects of Iran’s nuclear program to secure commitments to take on ISIL,” White House Press Secretary Josh Earnest said Monday, using an alternate acronym for the Islamic State. “These two issues are entirely separate.”

But, even before the Islamic State aspect surfaced, Republicans already had voiced concern that Washington may be softening its negotiating position in the nuclear talks.

In a letter sent to Kerry on Friday, 31 Republican senators expressed grave concerns about the new negotiations.